From a New York Times story by Ian Prasad Philbrick headlined “A Brief History of Consequential Deaths in Congress”:

Dianne Feinstein, who died on Thursday at 90, was the first senator to die in office since John McCain in 2018.

But since the first Congress convened in 1789, deaths in office have been a fairly regular occurrence. “You look back in history, nearly one in 10 members of Congress have,” Jane L. Campbell, the president of the U.S. Capitol Historical Society, told me.